Ion source

ABSTRACT

An ion source includes a plasma generating chamber into which an ionization gas containing fluorine is introduced, a hot cathode provided on one side in the plasma generating chamber, an opposing reflecting electrode which is provided on other side in the plasma generating chamber and reflects electrons when a negative voltage is applied from a bias power supply to the opposing reflecting electrode, and a magnet for generating a magnetic field along a line, which connects the hot cathode and the opposing reflecting electrode, in the plasma generating chamber. The opposing reflecting electrode is formed of an aluminum containing material.

TECHNICAL FIELD

The present disclosure relates to an ion source which is employed in anion implantation apparatus that implants aluminum ions into a targetsuch as a silicon carbide (SiC) substrate, or the like, for example, andgenerates an ion beam containing the aluminum ions.

RELATED ART

An example of the ion source of this type is set forth in PatentLiterature 1.

In the related-art ion source set forth in Patent Literature 1, a plateformed of the aluminum containing material (e.g., aluminum oxide) isprovided in the ionization chamber apart from an electrode (cathode) anda recoil plate as the components used for the plasmageneration/confinement, and the plasma being generated by ionizing afluoride gas (e.g., silicon tetrafluoride) is caused to erode the plateformed of the aluminum containing material such that the aluminum ionsare emitted into the plasma.

[Related Art Literature]

[Patent Literature]

-   [Patent Literature 1] Japanese Patent No. 3325393 (paragraphs    0006-0011, 0016-0021, FIG. 1, FIG. 2)

In the related-art ion source, the plate formed of the aluminumcontaining material and used exclusively to generate the aluminum ionsmust be provided apart from the components used for the plasmageneration/confinement. Therefore, such a problem exists that the numberof items is increased correspondingly and a structure becomescomplicated.

SUMMARY

Exemplary embodiments of the present invention to provide an ion sourcethat generates an ion beam containing aluminum ions, in which areduction of the number of items and a simplification of the structurein the ion source can be attained.

An ion source for generating an ion beam containing an aluminum ion,according to an exemplary embodiment of the invention, includes:

a plasma generating chamber which is also used as an anode and generatesa plasma in an interior, and into which an ionization gas containingfluorine is introduced;

a hot cathode provided on one side in the plasma generating chamber andisolated electrically from the plasma generating chamber;

an opposing reflecting electrode which is provided on other side in theplasma generating chamber to oppose to the hot cathode and is isolatedelectrically from the plasma generating chamber, to which a voltage thatis negative in contrast to a potential of the plasma generating chamberis applied, and which reflects electrons in the plasma generatingchamber and is formed of an aluminum containing material; and

a magnet which generates a magnetic field along a line connecting thehot cathode and the opposing reflecting electrode, in the plasmagenerating chamber.

In place of the application of the negative voltage to the opposingreflecting electrode, the opposing reflecting electrode may be set to afloating potential.

According to the exemplary embodiment of the invention, the aluminumparticles such as the aluminum ions, etc. can be emitted into the plasmafrom the opposing reflecting electrode that has a function of reflectingthe electrons in the plasma generating chamber such that the aluminumions can be contained in the plasma. Therefore, unlike the foregoing ionsource in the related art, there is no need to provide particularly theplate that is used exclusively to generate the aluminum ions. As aresult, a reduction of the number of items and a simplification of thestructure of the ion source can be attained.

Also, the magnet for generating the magnetic field along the line thatconnects the hot cathode and the opposing reflecting electrode isprovided. Therefore, the electrons in the plasma generating chamberreciprocally moves between the hot cathode and the opposing reflectingelectrode, so that the high-density plasma can be generated between thehot cathode and the opposing reflecting electrode. The opposingreflecting electrode is positioned at the edge portion of suchhigh-density plasma, and the plasma is ready to move in the directionalong the magnetic field and the opposing reflecting electrode ispositioned at the edge portion in the easily moving direction.Therefore, the opposing reflecting electrode is exposed effectively tothe high-density plasma. Accordingly, the aluminum particles such as thealuminum ions, or the like can be emitted effectively into the plasmafrom the opposing reflecting electrode. As a result, it is made easy toincrease an amount of aluminum ions contained in the ion beam.

The above-mentioned ion source further includes:

a backside reflecting electrode which is provided at a back of anelectron emitting portion of the hot cathode in the plasma generatingchamber to oppose to the opposing reflecting electrode, which isisolated electrically from the plasma generating chamber, to which avoltage that is negative in contrast to the potential of the plasmagenerating chamber is applied, and which reflects the electrons in theplasma generating chamber and is formed of an aluminum containingmaterial.

In place of the application of the negative voltage to the backsidereflecting electrode, the backside reflecting electrode may be set to afloating potential.

According to the exemplary embodiment of the invention, furtheradvantages described hereunder can be achieved. That is, the aluminumparticles are emitted into the plasma not only from the opposingreflecting electrode but also the backside reflecting electrode by theerosion, the sputtering, and the like caused by the fluorine ions in theplasma. Therefore, an amount of aluminum ions contained in the ion beamcan be increased by increasing an amount of aluminum particles that areemitted into the plasma.

Also, the hot cathode is provided in vicinity of the backside reflectingelectrode, and thus a temperature of the backside reflecting electrodeis increased by a radiant heat from the hot cathode. As a result, animprovement of a sputter ratio and an increase of a vapor pressure ofthe aluminum containing material can be expected, and thus an amount ofaluminum particles that are emitted into the plasma can be increased.Therefore, an amount of aluminum ions contained in the ion beam can beincreased from this viewpoint.

Also, in the case of this invention, the backside reflecting electrodehaving a function of reflecting the electrons in the plasma generatingchamber is also used as the aluminum particle emitting electrode.Therefore, unlike the ion source in the related art, there is nonecessity that the plate used exclusively to generate the aluminum ionsshould be particularly provided. As a result, a reduction of the numberof items and a simplification of the structure of the ion source can beattained in contact to the case where such plate is particularlyprovided.

In the above-mentioned ion source, the hot cathode is an indirectlyheated type hot cathode which has a cathode member which emits thermionsby a heating and a filament which heats the cathode member, the cathodemember being arranged in an opening portion of the plasma generatingchamber, and

a wall surface containing the opening portion of the plasma generatingchamber is formed of an electric insulating aluminum containingmaterial.

The wall surface containing the opening portion of the plasma generatingchamber may be formed of an aluminum containing material.

Alternatively, the wall surface formed of an aluminum containingmaterial may be set to a floating potential or, a voltage that isnegative in contrast to the potential of the plasma generating chambermay be applied to the wall surface.

According to the exemplary embodiment of the invention, furtheradvantages described hereunder can be achieved. That is, the aluminumparticles are emitted into the plasma not only from the opposingreflecting electrode but also the wall surface formed of the aluminumcontaining material of the plasma generating chamber by the erosion, thesputtering, and the like caused by the fluorine ions in the plasma.Therefore, an amount of aluminum ions contained in the ion beam can beincreased by increasing an amount of aluminum particles that are emittedinto the plasma.

Also, the hot cathode is provided in vicinity of the wall surface formedof the aluminum containing material, and thus a temperature of the wallsurface formed of the aluminum containing material is increased by aradiant heat from the hot cathode. As a result, an improvement of asputter ratio and an increase of a vapor pressure of the aluminumcontaining material can be expected, and thus an amount of aluminumparticles that are emitted into the plasma can be increased. Therefore,an amount of aluminum ions contained in the ion beam can be increasedfrom this viewpoint.

Also, in the case of this invention, a part of the wall surfaceconstituting the aluminum generating chamber, i.e., the wall surfacecontaining the opening portion, is also used as the aluminum particleemitting electrode. Therefore, unlike the ion source in the related art,there is no necessity that the plate used exclusively to generate thealuminum ions should be particularly provided. As a result, a reductionof the number of items and a simplification of the structure of the ionsource can be attained in contact to the case where such plate isparticularly provided.

Other features and advantages may be apparent from the followingdetailed description, the accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an embodiment of an ionsource according to this invention.

FIG. 2 is a schematic sectional view showing another embodiment of anion source according to this invention.

FIG. 3 is a schematic sectional view showing an embodiment when a hotcathode is of an indirectly heated type.

FIG. 4 is a schematic sectional view showing still another embodiment ofan ion source according to this invention.

FIG. 5 is a schematic sectional view showing another embodiment when ahot cathode is of an indirectly heated type.

FIG. 6 is a schematic sectional view showing still another embodimentwhen a hot cathode is of an indirectly heated type.

FIG. 7 is a schematic sectional view showing further embodiment when ahot cathode is of an indirectly heated type.

DETAILED DESCRIPTION

FIG. 1 is a schematic sectional view showing an embodiment of an ionsource according to this invention. This ion source is the ion sourcethat generates (extracts out) an ion beam 34 containing aluminum ions,and is equipped with a plasma generating chamber 2 that is used togenerate a plasma 4 in an interior and also serves as an anode for anarc discharge. This plasma generating chamber 2 is shaped into arectangular parallelepiped, for example, but the shape is not limited tothis shape.

An ionization gas 8 containing fluorine is introduced into the plasmagenerating chamber 2 through a gas inlet port 6. The position of the gasinlet port 6 is not limited to a position in the illustrate example. Thereason why the ionization gas 8 containing fluorine is used is that,since the fluorine has a very strong chemical action and has a strongreactivity with other materials, the plasma 4 generated by ionizing theionization gas 8 containing fluorine has a strong action to emitaluminum particles such as aluminum ions, or the like from an opposingreflecting electrode 20 described later.

As the ionization gas 8 containing fluorine, a fluoride gas such asboron fluoride (BF₃), silicon tetrafluoride (SiF₄), germanium fluoride(GeF₄), or the like, or a gas containing fluorine (F₂), for example, isemployed. As the ionization gas 8 containing fluorine, for example, thefluoride gas itself or the fluorine itself may be employed, or theirdiluted gas diluted with an appropriate gas (e.g., helium gas) may beemployed.

A hot cathode 12 is provided on one side in the plasma generatingchamber 2. This hot cathode 12 is electrically isolated from the plasmagenerating chamber 2, and emits thermions into the plasma generatingchamber 2.

As the hot cathode 12, the directly heated type as shown in thisembodiment may be employed or the indirectly heated type as shown in anembodiment described later (see FIG. 3, or the like) may be employed.

In this embodiment, the hot cathode 12 is a U-shaped filament, and iselectrically isolated from the plasma generating chamber 2 with aninsulator 14. In this case, a direction of the filament is shown forconvenience sake to clarify the connection to a DC heating power supply16. Actually, this filament is arranged such that a plane containing theU-shaped filament is positioned in substantially parallel with an ionextracting port 10 described later. This is also true in anotherembodiment shown in FIG. 2. In this case, the filament may be shapedother than the U-shape.

The DC heating power supply 16 for heating the hot cathode 12 isconnected across the hot cathode 12. A DC arc power supply 18 isconnected between one end of the hot cathode 12 and the plasmagenerating chamber 2 such that its positive electrode side is directedto the plasma generating chamber 2. This arc power supply 18 applies anarc voltage V_(A) between the hot cathode 12 and the chamber 2 togenerate an arc discharge in such a manner that the ionization gas 8introduced into the plasma generating chamber 2 is ionized to generatethe plasma 4.

The opposing reflecting electrode 20 is provided on the other side (theopposite side to the hot cathode 12) in the plasma generating chamber 2.This opposing reflecting electrode 20 is provided to oppose to the hotcathode 12, and has a function of reflecting (in other words, repellingor repulsing. Ditto with the followings) the electrons in the plasmagenerating chamber 2 (mainly, the thermions emitted from the hot cathode12. Ditto with the followings). This opposing reflecting electrode 20 isisolated electrically from the plasma generating chamber 2 with aninsulator 22.

In this embodiment, a bias voltage V_(B) that is negative in contrast toa potential of the plasma generating chamber 2 is applied to theopposing reflecting electrode 20 from a DC bias power supply 24. Amagnitude of the bias voltage V_(B) may be decided with regard to abalance among an action of reflecting the electrons by the opposingreflecting electrode 20, an action of emitting the aluminum particlessuch as the aluminum ions, or the like from the opposing reflectingelectrode 20, an action of sputtering the surface of the opposingreflecting electrode 20 by the ions in the plasma 4, etc. From suchviewpoint, it is preferable that a magnitude of the bias voltage V_(B)should be set to about 40 V to 150 V, for example. When the ionizationgas 8 is the gas containing the boron fluoride (BF₃), the magnitude ofabout 60 V to 120 V out of them is more preferable.

The opposing reflecting electrode in the publicly known ion source isformed of a refractory metal such as titanium (Ti), tantalum (Ta),molybdenum (Mo), or the like, or their alloy. But the above opposingreflecting electrode 20 is formed of the aluminum containing material.The aluminum containing material is an aluminum compound such asaluminum oxide (Al₂O₃), aluminum nitride (AlN), or the like, forexample. Also, the aluminum (Al) can be employed when a temperaturecontrol is applied.

A magnet 30 is provided on the outside of the plasma generating chamber2. The magnet 30 generates a magnetic field 28 along a line 26 thatconnects the hot cathode 12 and the opposing reflecting electrode 20.The magnet 30 is formed of an electromagnet, for example, but apermanent magnet may also be employed. A direction of the magnetic field28 may be set in the opposite direction to that in the illustratedexample.

Because of the foregoing presence of the opposing reflecting electrode20 and the magnetic field 28, the electrons in the plasma generatingchamber 2 move reciprocally between the hot cathode 12 and the opposingreflecting electrode 20 while turning in the magnetic field 28 around anaxis in the direction of the magnetic field 28. As a result, a collisionprobability between the electrons and gas molecules of the ionizationgas 8 is enhanced, then an ionization efficiency of the ionization gas 8is increased, and thus a generation efficiency of the plasma 4 isincreased. More concretely, the high-density plasma 4 can be generatedbetween the hot cathode 12 and the opposing reflecting electrode 20.

The ion extracting port 10 used to extract out the ions from the plasma4 is provided in the wall surface of the plasma generating chamber 2. Inthis embodiment, the ion extracting port 10 has a long and narrow shapein the direction along the line 26. More concretely, this port 10 isshaped into a long slit in the direction along the line 26. However, theshape of the ion extracting port 10 is not limited to this shape.

A extracting electrode system 32 is provided near the outlet of the ionextracting port 10. The extracting electrode system 32 is used toextract out the ion beam 34 from the plasma generating chamber 2 (moreconcretely, from the plasma 4 generated there). The extracting electrodesystem 32 is constructed by a sheet of electrode in the illustratedexample. But this extracting electrode system 32 is not limited to this,and this extracting electrode system 32 may be constructed by pluralsheets of electrodes.

In this ion source, the opposing reflecting electrode 20 formed of thealuminum containing material is exposed to the plasma 4 that isgenerated by ionizing the ionization gas 8 containing the fluorine. Onaccount of the erosion caused by the fluorine ion, the fluorine radical,and the like in the plasma 4, the sputtering caused by the ions such asthe fluorine ion, and the like in the plasma 4, etc., the aluminumparticles such as the aluminum ions, or the like are emitted from theopposing reflecting electrode 20, and the aluminum ions are contained inthe plasma 4. The aluminum particles emitted from the opposingreflecting electrode 20 may be emitted as the aluminum ions or emittedas the neutral aluminum atoms. The neutral aluminum atoms collide withthe electrons in the plasma 4 to some extent, and are ionized into thealuminum ions. In this manner, the aluminum ions (e.g., Al⁺, Al²⁺, Al³⁺.Ditto with the followings) are contained in the plasma 4. As a result,the ion beam 34 containing the concerned aluminum ions can be generated.

In this manner, according to this ion source, the aluminum particlessuch as the aluminum ions, and the like can be emitted into the plasma 4from the opposing reflecting electrode 20 that has a function ofreflection the electrons in the plasma generating chamber 2, and thealuminum ions can be contained in the plasma 4. In other words, theopposing reflecting electrode 20 that reflects the electrons in theplasma generating chamber 2 is also used for the purpose of emitting thealuminum particles. Therefore, unlike the foregoing ion source in therelated art, there is no need to provide particularly the plate that isused exclusively to generate the aluminum ions. As a result, a reductionof the number of items and a simplification of the structure of the ionsource can be attained.

In addition, the magnet 30 for generating the magnetic field 28 alongthe line 26 that connects the hot cathode 12 and the opposing reflectingelectrode 20 is provided. Therefore, the electrons in the plasmagenerating chamber 2 moves reciprocally between the hot cathode 12 andthe opposing reflecting electrode 20, as described above. The plasma 4can be generated at a high density between the hot cathode 12 and theopposing reflecting electrode 20. The opposing reflecting electrode 20is positioned at the end portion of such high-density plasma 4, theplasma 4 is easily movable in the direction along the magnetic field 28,and the opposing reflecting electrode 20 is positioned at the endportion in the easily movable direction. Therefore, the opposingreflecting electrode 20 can be exposed effectively to the high-densityplasma 4. Accordingly, the aluminum particles such as the aluminum ions,and the like can be emitted effectively into the plasma 4 from theopposing reflecting electrode 20. As a result, it can be made easy thatan amount of aluminum ions contained in the ion beam 34 is increased.

In the foregoing ion source in the related art, the plate formed of thealuminum containing material is fitted on the bottom surface of theionization chamber. The opposing reflecting electrode 20 can be exposedmore effectively to the plasma 4 than the plate located in such positionin connection to the magnetic field 28. Therefore, the aluminumparticles such as the aluminum ions, and the like can be emitted moreeffectively into the plasma 4. In turn, the ion beam 34 containing alarger amount of aluminum ions can be generated.

Normally, the unnecessary particles are stacked on the surfaces, whichare exposed to the plasma 4, including the surface of the opposingreflecting electrode 20 along with the operation of the ion source,i.e., along with the generation of the plasma 4. When the opposingreflecting electrode 20 is observed particularly, the bias voltage V_(B)that is negative with respect to the plasma generating chamber 2 isapplied to the opposing reflecting electrode 20. Therefore, the opposingreflecting electrode 20 can achieve the action of accelerating the ionsin the plasma 4 by the bias voltage V_(B) to pull in them, in additionto the above action of reflecting the electrons. The particles stackedon the surface of the opposing reflecting electrode 20 are sputtered bythe accelerated ions, and thus the surface of the opposing reflectingelectrode 20 can be cleaned. Therefore, the action of exposing thesurface itself of the opposing reflecting electrode 20 and emitting thealuminum particles from the surface can be maintained stably for alonger time.

In contrast, the foregoing ion source in the related art is notconstructed such that the negative voltage in contrast to the ionizationchamber is applied to the plate formed of the aluminum containingmaterial (or this plate is set to a floating potential). Therefore, suchan action is not expected that the particles stacked on the surface ofthe concerned plate are sputtered by the accelerated ions and thus thesurface of the concerned plate is cleaned. As a result, a function ofemitting the aluminum particles from the concerned plate is quicklylowered.

The opposing reflecting electrode 20 is exhausted after the aluminumparticles are emitted from the opposing reflecting electrode 20.Therefore, the opposing reflecting electrode 20 may be exchanged asoccasion demands. This respect is similar to the case of the plate inthe foregoing ion source in the related art.

By the way, when the aluminum ions are implanted into the target such asthe silicon carbide substrate, or the like by using this ion source asthe ion implantation apparatus, a mass separator that selects thealuminum ions of a necessary momentum by separating a momentum (e.g.,mass) of the ion beam 34 may be provided between the ion source and thetarget, as occasion demands. This is also true of the case where the ionsource in the embodiment described hereunder is employed.

Next, several other embodiments of the ion source according to thisinvention will be explained hereunder. Here, in the explanation ofrespective following embodiments, the same reference symbols are affixedto the same or equivalent portions as or to those in the embodimentexplained previously (for example, the embodiment shown in FIG. 1).Mainly differences from the embodiment explained previously will beexplained hereunder.

Instead of the provision of the above bias power supply 24, the opposingreflecting electrode 20 may be connected to the hot cathode 12 and maybe fixed at the cathode potential, like the embodiment shown in FIG. 2.More concretely, the opposing reflecting electrode 20 may be connectedto (a) connection portion a between the negative electrode of theheating power supply 16 and one end of the hot cathode 12, like theexample shown in FIG. 2, or (b) a connection portion b between thepositive electrode of the heating power supply 16 and the other end ofthe hot cathode 12 (i.e., the negative electrode of the arc power supply18). In either case, the negative voltage that is negative in contrastto the potential of the plasma generating chamber 2 can be applied tothe opposing reflecting electrode 20. Concretely, in the case of (a),the negative voltage of a magnitude of V_(A)+V_(H) can be applied and,in the case of (b), the negative voltage of a magnitude of V_(A) can beapplied. Where V_(A) denotes an arc voltage as the output voltage of thearc power supply 18, and V_(H) denotes the output voltage of the heatingpower supply 16. A magnitude of the arc voltage V_(A) is set to about 40V to 120 V, for example, and a magnitude of the output voltage V_(H) isset to about 2 V to 4 V, for example.

In the case of (a), the heating power supply 16 and the arc power supply18 are also used as the DC power supply that applies the negativevoltage to the opposing reflecting electrode 20. In the case of (b), thearc power supply 18 is also used as the DC power supply that applies thenegative voltage to the opposing reflecting electrode 20. The AC powersupply may be employed as the heating power supply 16. In such case, theabove (b) may be employed.

In the case of this embodiment, the negative voltage that is negative incontrast to the potential of the plasma generating chamber 2 can beapplied to the opposing reflecting electrode 20. Therefore, the almostsimilar advantages of the opposing reflecting electrode 20 to the casein the embodiment shown in FIG. 1 can be achieved.

In place of the application of the negative voltage to the opposingreflecting electrode 20, the opposing reflecting electrode 20 may not beconnected electrically to any portion and may be set to a floatingpotential. Even when the opposing reflecting electrode 20 is set to afloating potential, the electrons whose mass is lighter than the ions inthe plasma 4 and whose mobility is higher that such ions are incident onthe opposing reflecting electrode 20 in an amount that is greater thanthe ions. Therefore, the opposing reflecting electrode 20 is chargednegatively, and the similar action to the case where the negativevoltage is applied to the opposing reflecting electrode 20 can beachieved. That is, the substantially similar advantages of the opposingreflecting electrode 20 to those in the case of the embodiments shown inFIG. 1 and FIG. 2 can be achieved.

Here, (a) the bias power supply 24 is provided like the embodiment shownin FIG. 1, (b) the opposing reflecting electrode 20 is connected to thehot cathode 12 like the embodiment shown in FIG. 2, and (c) the opposingreflecting electrode 20 is not connected to any portion and is set to afloating potential are compared mutually. In the case of (a), the biasvoltage V_(B) can be chosen freely, and therefore the optimum voltagefor the aluminum ion generation, and the like can be applied easily tothe opposing reflecting electrode 20. In the case of (b), the arc powersupply 18, etc. are also used as the power supply that is used to applythe negative voltage to the opposing reflecting electrode 20. Therefore,the power supply used exclusively for the opposing reflecting electrode20 is not needed, and thus a configuration of the power supply can besimplified. Also, a potential of the opposing reflecting electrode 20can be fixed. In the case of (c), the power supply used exclusively forthe opposing reflecting electrode 20 is not needed, and thus aconfiguration of the power supply can be simplified. It is possible tosay that the similar situation is true of other embodiments describedlater.

As described later, the indirectly heated type may be employed as thehot cathode 12. An example is shown in FIG. 3.

The hot cathode 12 has a cathode member 36 for emitting the thermionswhen heated, and a filament 38 for heating the cathode member 36. Aconcrete structure that the cathode member 36 and the filament 38 arearranged in the plasma generating chamber 2 is shown in FIG. 3 in asimplified mode. The publicly known structure as set forth in JapanesePatent No. 3758667, for example, may be employed. This is similarlyapplied to the embodiments shown in FIG. 5 to FIG. 7.

A DC heating power supply 40 for heating the filament 38 is connected tothe filament 38. ADC bombard power supply 42 is connected between thefilament 38 and the cathode member 36 to direct its positive electrodeside to the cathode member 36. This bombard power supply 42 acceleratesthe thermions emitted from the filament 38 toward the cathode member 36and heats the cathode member 36 by utilizing the impact of thethermions. The above-mentioned arc power supply 18 is connected betweenthe cathode member 36 and the plasma generating chamber 2.

When the indirectly heated hot cathode 12 is provided, the bias voltageV_(B) may be applied to the opposing reflecting electrode 20 or theopposing reflecting electrode 20 may be connected to the hot cathode 12and may be fixed at the cathode potential. More concretely, the opposingreflecting electrode 20 may be connected to (a) a connection portion cbetween the negative electrode of the heating power supply 40 and oneend of the filament 38, (b) a connection portion d between the positiveelectrode of the heating power supply 40 and the other end of thefilament 38, and (c) a connection portion e between the cathode member36 and the arc power supply 18 (i.e., the negative electrode of the arcpower supply 18), as indicated with a chain double-dashed line in FIG.3. In either case, the negative voltage that is negative in contrast tothe potential of the plasma generating chamber 2 can be applied to theopposing reflecting electrode 20. Concretely, the negative voltage of amagnitude of V_(A)+V_(D)+V_(F) can be applied in the case of (a), thenegative voltage of a magnitude of V_(A)+V_(D) can be applied in thecase of (b), and the negative voltage of a magnitude of V_(A) can beapplied in the case of (c). Where V_(A) denotes the above arc voltage,V_(D) denotes the output voltage of the bombard power supply 42, andV_(F) denotes the output voltage of the heating power supply 40. Amagnitude of the arc voltage V_(A) is set to about 40 V to 120 V asdescribed above, for example, a magnitude of the output voltage V_(F) isset to about 2 V to 4 V, for example, and a magnitude of the outputvoltage V_(D) is set to about 300 V to 600 V, for example.

In the case of (a), the arc power supply 18, the bombard power supply42, and the heating power supply 40 are also used as the DC power supplythat applied the negative voltage to the opposing reflecting electrode20. In the case of (b), the arc power supply 18 and the bombard powersupply 42 are also used as the DC power supply that applied the negativevoltage to the opposing reflecting electrode 20. In the case of (c), thearc power supply 18 is also used as the DC power supply that applied thenegative voltage to the opposing reflecting electrode 20. An AC powersupply may also be employed as the heating power supply 40. In suchcase, the above case of (b) or (c) may be employed.

Meanwhile, as set forth in Japanese Patent No. 3797160, for example,some ion sources are equipped with the reflecting electrode (backsidereflecting electrode) on the hot cathode side, in addition to theopposing reflecting electrode 20. In this case, as described above, bothreflecting electrodes in the publicly known ion source are formed of notthe aluminum containing material but a refractory metal or its alloy. Anembodiment of an embodiment in which a backside reflecting electrodecorresponding to the backside reflecting electrode is further providedis shown in FIG. 4.

In the ion source of this embodiment, a backside reflecting electrode 44equipped with a function of reflecting the electrons in the plasmagenerating chamber 2 is further provided at the back of the electronemitting portion of the hot cathode 12 in the plasma generating chamber2. This backside reflecting electrode 44 is provided to oppose to theopposing reflecting electrode 20, and is isolated electrically from theplasma generating chamber 2. The negative voltage that is negative incontrast to the potential of the plasma generating chamber 2 is appliedto the backside reflecting electrode 44 (or the backside reflectingelectrode 44 is set to a floating potential, as described above). Thisbackside reflecting electrode 44 is formed of the aluminum containingmaterial, as described above.

As the means for supporting the backside reflecting electrode 44 in theplasma generating chamber 2 while isolating electrically from the plasmagenerating chamber 2, the publicly known means can be employed. In thisembodiment, the backside reflecting electrode 44 is supported by aninsulator 48, which is also used as a current introducing terminal, asan example, but the supporting means is not limited to this. In anembodiment shown in FIG. 5, an illustration of the supporting means ofthe backside reflecting electrode 44 is omitted.

The electron emitting portion of the hot cathode 12 denotes the portion,which emits particularly many thermions, of the hot cathode 12.Concretely, the electron emitting portion corresponds to a top endportion of the hot cathode 12 (a top end portion on the inside of theplasma generating chamber 2). In the case of the indirectly heated typehot cathode 12, the electron emitting portion corresponds to a top endportion of the cathode member 36 (a top end portion on the inside of theplasma generating chamber 2).

In this embodiment, the backside reflecting electrode 44 has a hole 46through which the hot cathode 12 (more concretely, its leg portion)passes while keeping electric insulation. A clearance of about 3 mm, forexample, is provided between the hot cathode 12 and the backsidereflecting electrode 44. Therefore, it is possible to say that thebackside reflecting electrode 44 is provided in vicinity of the hotcathode 12.

In this event, (a) the bias voltage V_(B) that is negative in contrastto the potential of the plasma generating chamber 2 may be applied tothe backside reflecting electrode 44 from the bias power supply 24 whileusing the bias power supply 24 commonly as the opposing reflectingelectrode 20, like the example shown in FIG. 4, or (b) the bias voltagethat is negative in contrast to the potential of the plasma generatingchamber 2 may be applied to the backside reflecting electrode 44 fromthe DC bias power supply that is different from the bias power supply24, or (c) the voltage that is negative in contrast to the potential ofthe plasma generating chamber 2 may be applied to the backsidereflecting electrode 44 by connecting the backside reflecting electrode44 to the connection portion a or b, like the case of the opposingreflecting electrode 20 shown in FIG. 2.

Alternately, instead of the application of the negative voltage to thebackside reflecting electrode 44, the backside reflecting electrode 44may not be connected to any portion and may be set at a floatingpotential. Even when the backside reflecting electrode 44 is set to afloating potential, the electrons whose mass is lighter than the ions inthe plasma 4 and whose mobility is higher that such ions are incident onthe backside reflecting electrode 44 in an amount that is greater thanthe ions, like the case of the opposing reflecting electrode 20 that isset at a floating potential. Therefore, the backside reflectingelectrode 44 is charged negatively, and the similar action to the casewhere the negative voltage is applied to the backside reflectingelectrode 44 can be achieved.

That is, like the case of the opposing reflecting electrode 20, thebackside reflecting electrode 44 can perform an action of reflecting theelectrons in the plasma generating chamber 2.

In addition, the backside reflecting electrode 44 is exposed to theplasma 4, which is generated by ionizing the ionization gas 8 containingthe fluorine, during the operation of the ion source. In addition, thebackside reflecting electrode 44 is formed of the aluminum containingmaterial. Therefore, according to the similar action to that describedwith respect to the opposing reflecting electrode 20, i.e., on accountof the erosion caused by the fluorine ion, the fluorine radical, and thelike in the plasma 4, the sputtering caused by the ions such as thefluorine ion, and the like in the plasma 4, etc., the aluminum particlesare emitted from the backside reflecting electrode 44 into the plasma 4.In other words, areas of the aluminum containing material, which undergothe erosion or the sputtering by the fluorine ions, etc. in the plasma4, can be increased rather than the case where only the opposingreflecting electrode 20 is formed of the aluminum containing material.As a result, an amount of aluminum ions contained in the ion beam 34,i.e., an amount of aluminum ion beam, can be increased by increasing anamount of aluminum particles that are emitted into the plasma 4.

Also, the hot cathode 12 is provided in vicinity of the backsidereflecting electrode 44, as described above, and a temperature of thebackside reflecting electrode 44 is increased by a radiant heat from thehot cathode 12. As a result, an improvement of a sputter ratio and anincrease of a vapor pressure of the aluminum containing material can beexpected, and thus an amount of aluminum particles that are emitted intothe plasma 4 can be increased. Therefore, an amount of aluminum ionscontained in the ion beam 34 can be increased from this viewpoint.

In short, the reason why an improvement of a sputter ratio of thebackside reflecting electrode 44 can be expected when heated to a hightemperature is that a lattice vibration the aluminum atoms and otheratoms of the aluminum containing material constituting the backsidereflecting electrode 44 becomes active when heated to a hightemperature, and thus a chemical bond between these atoms is easily cutand the aluminum particles are ready to run out.

Also, the reason why an increase of a vapor pressure of the aluminumcontaining material can be expected when heated to a high temperature isthat, when the backside reflecting electrode 44 is heated to a hightemperature, the aluminum particles are easily emitted from the aluminumcontaining material into the atmosphere (i.e., the vacuum atmosphere inthe plasma generating chamber 2) along with the similar phenomenon thatis produced in an increase of a vapor pressure. Therefore, although thealuminum particle being emitted from the aluminum containing materialconstituting the backside reflecting electrode 44 along with the aboveaction is not strictly defined as a vapor, such event is mentioned as anincrease of a vapor pressure like the case of vapor.

Also, in the case of the embodiment, the backside reflecting electrode44 equipped with a function of reflecting the electrons in the plasmagenerating chamber 2 is also used as the aluminum particle emittingelectrode. Therefore, unlike the ion source in the related art, there isno need that the plate used exclusively to generate the aluminum ionsshould be particularly provided. As a result, a reduction of the numberof items and a simplification of the structure of the ion source can beattained in contrast to the case where such plate is particularlyprovided.

Such an embodiment is shown in FIG. 5 that the above the backsidereflecting electrode 44 is provided in addition to the opposingreflecting electrode 20 and also the hot cathode 12 is the indirectlyheated type.

This hot cathode 12 has an almost similar structure to that of the hotcathode 12 shown in FIG. 3. But the cathode member 36 is arranged in theplasma generating chamber 2 in this embodiment. Also, the backsidereflecting electrode 44 that is electrically isolated from the plasmagenerating chamber 2 is provided at the back of the electron emittingportion of the hot cathode 12 (i.e., as described above, the top endportion of the cathode member 36) to oppose to the opposing reflectingelectrode 20 (see FIG. 4, etc.). In other words, it is possible to saythat the backside reflecting electrode 44 is provided at the side backof the top end portion of the cathode member 36. This provision iscontained in the term “back” in this specification.

In this embodiment, the backside reflecting electrode 44 has the hole 46through which the cathode member 36 passes while keeping electricinsulation. A clearance of about 3 mm, for example, is provided betweenthe cathode member 36 and the backside reflecting electrode 44.Therefore, it is possible to say that the backside reflecting electrode44 is provided in vicinity of the hot cathode 12, more concretely, thecathode member 36.

In this embodiment, the negative voltage that is negative in contrast tothe potential of the plasma generating chamber 2 may be applied to thebackside reflecting electrode 44 like the case of the embodiment shownin FIG. 4, or the backside reflecting electrode 44 may not be connectedelectrically to any portion and may be set at a floating potential. Whenthe negative voltage is to be applied, (a) the negative bias voltageV_(B) may be applied from the bias power supply 24, (b) the negativebias voltage may be applied from the DC bias power supply different fromthe bias power supply 24, or (c) the backside reflecting electrode 44may be connected to the connection portion e, d, or c, like the case ofthe embodiment shown in FIG. 3. Indeed, there is no necessity that, whenthe backside reflecting electrode 44 fulfills the similar action to thatexplained in the embodiment in FIG. 4, the negative voltage that islarge enough to contain the output voltage V_(D) should be applied tothe backside reflecting electrode 44. Therefore, when the backsidereflecting electrode 44 is connected to the connection portion e and thearc voltage V_(A) is applied thereto, the bias voltage has sufficientamplitude.

In the case of this embodiment, the almost similar advantages of thebackside reflecting electrode 44 to those explained in the embodiment inFIG. 4 can be attained. That is, in addition to the action of reflectingthe electrons in the plasma generating chamber 2, an amount of aluminumions contained in the ion beam 34 (see FIG. 4) can be increased byincreasing an amount of aluminum particles being emitted into the plasma4. Such an event is similar to the above that, because the hot cathode12 is located in the neighborhood, a temperature of the backsidereflecting electrode 44 is increased and thus an amount of aluminumparticles emitted into the plasma 4 is increased. Also, the backsidereflecting electrode 44 is also used as the electrode that is used toemit the aluminum particles. As a result, a reduction of the number ofitems and a simplification of the structure of the ion source can beattained.

In an embodiment shown in FIG. 6, the cathode member 36 of the hotcathode 12 is arranged in an opening portion 3 of the plasma generatingchamber 2. A wall surface 2 a containing the opening portion 3 (moreconcretely, one side surface containing the opening portion 3) of theplasma generating chamber 2 is composed of the electric insulatingaluminum containing material. The electric insulating aluminumcontaining material is the aluminum compound such as aluminum oxide(Al₂O₃), aluminum nitride (AlN), or the like, for example.

The wall surface 2 a composed of the aluminum containing material iselectrically isolative, and thus is set at a floating potential. Likethe case of the backside reflecting electrode 44 at the floatingpotential described above, the electrons whose mass is lighter than theions in the plasma 4 and whose mobility is higher that such ions areincident on the wall surface 2 a in an amount that is greater than theions. Therefore, the wall surface 2 a is charged negatively.

Accordingly, like the case of the backside reflecting electrode 44, thiswall surface 2 a can also attain the action of reflecting the electronsin the plasma generating chamber 2. In addition to this, such anadvantage can be attained that an amount of aluminum ions contained inthe ion beam 34 is increased by increasing an amount of aluminumparticles being emitted into the plasma 4. This advantage will beexplained together with an embodiment shown in FIG. 7.

In an embodiment shown in FIG. 7, the wall surface 2 a containing theopening portion 3 of the plasma generating chamber 2 is formed of thealuminum containing material, and is electrically isolated from theother wall surface of the plasma generating chamber 2 with interventionof an insulator 50. In this embodiment, the aluminum containing materialmay be electric isolative or conductive.

Like the case of the backside reflecting electrode 44 in the embodimentshown in FIG. 5, the negative voltage that is negative in contrast tothe potential of the plasma generating chamber 2 may be applied to thewall surface 2 a being composed of the aluminum containing material, orthe wall surface 2 a may not be connected electrically to any portionand may be set at a floating potential. When the negative voltage is tobe applied, (a) the negative bias voltage V_(B) may be applied from thebias power supply 24, (b) the negative bias voltage may be applied fromthe DC bias power supply different from the bias power supply 24, or (c)the wall surface 2 a may be connected to the connection portion e, d, orc. For example, the wall surface 2 a may be connected to the connectionportion e for the similar reason.

When the wall surface 2 a is set at a floating potential, the wallsurface 2 a can be charged negatively by the same action as that in thecase of the wall surface 2 a in the embodiment shown in FIG. 6.Therefore, the same advantages as those in the case where the negativevoltage is applied to the wall surface 2 a can be attained.

In other words, like the case of the backside reflecting electrode 44,or the like, the wall surface 2 a performs the action of reflecting theelectrons in the plasma generating chamber 2.

Further, in the case of both embodiments shown in FIG. 6 and FIG. 7, thewall surface 2 a composed of the aluminum containing material is exposedto the plasma 4, which is generated by ionizing the ionization gas 8containing the fluorine, during the operation of the ion source.Therefore, according to the similar action to that described withrespect to the opposing reflecting electrode 20 and the backsidereflecting electrode 44, i.e., on account of the erosion caused by thefluorine ion, the fluorine radical, and the like in the plasma 4, thesputtering caused by the ions such as the fluorine ion, and the like inthe plasma 4, etc., the aluminum particles are emitted from the wallsurface 2 a formed of the aluminum containing material into the plasma4. In other words, areas of the aluminum containing material, whichundergo the erosion or the sputtering by the fluorine ions, etc. in theplasma 4, can be increased in contrast to the case where only theopposing reflecting electrode 20 is formed of the aluminum containingmaterial. As a result, an amount of aluminum ions contained in the ionbeam 34, i.e., an amount of aluminum ion beams, can be increased byincreasing an amount of aluminum particles that are emitted into theplasma 4.

Also, the hot cathode 12 (concretely, the cathode member 36, etc.) isprovided in vicinity of the wall surface 2 a formed of the aluminumcontaining material, and a temperature of the wall surface 2 a isincreased by a radiant heat from the hot cathode 12. As a result, likethe case of the backside reflecting electrode 44, an improvement of asputter ratio of the wall surface 2 a and an increase of a vaporpressure of the aluminum containing material can be expected, and thusan amount of aluminum particles that are emitted into the plasma 4 canbe increased. Therefore, an amount of aluminum ions contained in the ionbeam 34 can be increased from this viewpoint.

Also, in the case of both embodiments shown in FIG. 6 and FIG. 7, a partof the wall surface constituting the plasma generating chamber 2, i.e.,the wall surface 2 a containing the opening portion 3, is also used asthe plate that is used to emit the aluminum particles. Therefore, unlikethe ion source in the related art, there is no need that the plate usedexclusively to generate the aluminum ions should be particularlyprovided. As a result, a reduction of the number of items and asimplification of the structure of the ion source can be attained ratherthan the case where such plate is particularly provided.

In the comparison between both embodiments in FIG. 6 and FIG. 7, sincethe insulator 50 is not needed, a structure in the embodiment in FIG. 6is simpler than that in the embodiment in FIG. 7. Conversely, since theinsulator 50 is provided, the electric isolation between the wallsurface 2 a and the other wall surface of the plasma generating chamber2 can be provided in the embodiment in FIG. 7 more surely than that inthe embodiment in FIG. 6.

Such a structure may be employed that a creeping distance is increasedby providing a groove, for example, on a surface of the insulator 50 onthe inside of the plasma generating chamber 2. With such structure, itcan be suppressed that the insulating performance is lowered due to acontamination on the surface of the insulator 50.

1. An ion source for generating an ion beam containing an aluminum ion,comprising: a plasma generating chamber which is also used as an anodeand generates a plasma in an interior, and into which an ionization gascontaining fluorine is introduced; a hot cathode provided on one side inthe plasma generating chamber and isolated electrically from the plasmagenerating chamber; an opposing reflecting electrode which is providedon other side in the plasma generating chamber to oppose to the hotcathode and is isolated electrically from the plasma generating chamber,to which a voltage that is negative in contrast to a potential of theplasma generating chamber is applied, and which reflects electrons inthe plasma generating chamber and is formed of an aluminum containingmaterial which is a solid state source, and is a first source ofimplantation ions; a magnet which generates a magnetic field along aline connecting the hot cathode and the opposing reflecting electrode,in the plasma generating chamber; and a gas inlet port configured tointroduce the ionization gas into the plasma generating chamber, whereinthe gas inlet port is connected to a wall of the plasma generatingchamber apart from the opposing reflecting electrode.
 2. An ion sourcefor generating an ion beam containing an aluminum ion, comprising: aplasma generating chamber which is also used as an anode and generates aplasma in an interior, and into which an ionization gas containingfluorine is introduced; a hot cathode provided on one side in the plasmagenerating chamber and isolated electrically from the plasma generatingchamber; an opposing reflecting electrode which is provided on otherside in the plasma generating chamber to oppose to the hot cathode andis isolated electrically from the plasma generating chamber, which isset at a floating potential, and which reflects electrons in the plasmagenerating chamber and is formed of an aluminum containing materialwhich is a solid state source, and is a first source of implantationions; a magnet which generates a magnetic field along a line connectingthe hot cathode and the opposing reflecting electrode, in the plasmagenerating chamber; and a gas inlet port configured to introduce theionization gas into the plasma generating chamber, wherein the gas inletport is connected to a wall of the plasma generating chamber apart fromthe opposing reflecting electrode.
 3. An ion source according to claim1, further comprising: a backside reflecting electrode which is providedat a back of an electron emitting portion of the hot cathode in theplasma generating chamber to oppose to the opposing reflectingelectrode, which is isolated electrically from the plasma generatingchamber, to which a voltage that is negative in contrast to thepotential of the plasma generating chamber is applied, and whichreflects the electrons in the plasma generating chamber and is formed ofan aluminum containing material which is a solid state source, and is asecond source of implantation ions.
 4. An ion source according to claim2, further comprising: a backside reflecting electrode which is providedat a back of an electron emitting portion of the hot cathode in theplasma generating chamber to oppose to the opposing reflectingelectrode, which is isolated electrically from the plasma generatingchamber, to which a voltage that is negative in contrast to thepotential of the plasma generating chamber is applied, and whichreflects the electrons in the plasma generating chamber and is formed ofan aluminum containing material which is a solid state source, and is asecond source of implantation ions.
 5. An ion source according to claim1, further comprising: a backside reflecting electrode which is providedat a back of an electron emitting portion of the hot cathode in theplasma generating chamber to oppose to the opposing reflectingelectrode, which is isolated electrically from the plasma generatingchamber, which is set at a floating potential, and which reflects theelectrons in the plasma generating chamber and is formed of an aluminumcontaining material which is a solid state source, and is a secondsource of implantation ions.
 6. An ion source according to claim 2,further comprising: a backside reflecting electrode which is provided ata back of an electron emitting portion of the hot cathode in the plasmagenerating chamber to oppose to the opposing reflecting electrode, whichis isolated electrically from the plasma generating chamber, which isset at a floating potential, and which reflects the electrons in theplasma generating chamber and is formed of an aluminum containingmaterial which is a solid state source, and is a second source ofimplantation ions.
 7. An ion source according to claim 1, wherein thehot cathode is an indirectly heated type hot cathode which has a cathodemember which emits thermions by a heating and a filament which heats thecathode member, the cathode member being arranged in an opening portionof the plasma generating chamber, and a wall surface containing theopening portion of the plasma generating chamber is formed of anelectric insulating aluminum containing material.
 8. An ion sourceaccording to claim 2, wherein the hot cathode is an indirectly heatedtype hot cathode which has a cathode member which emits thermions by aheating and a filament which heats the cathode member, the cathodemember being arranged in an opening portion of the plasma generatingchamber, and a wall surface containing the opening portion of the plasmagenerating chamber is formed of an electric insulating aluminumcontaining material.
 9. An ion source according to claim 1, wherein thehot cathode is an indirectly heated type hot cathode which has a cathodemember which emits thermions by a heating and a filament which heats thecathode member, the cathode member being arranged in an opening portionof the plasma generating chamber, and a wall surface containing theopening portion of the plasma generating chamber is formed of analuminum containing material, and is insulated electrically from otherwall surfaces of the plasma generating chamber with intervention of aninsulator and is set at a floating potential.
 10. An ion sourceaccording to claim 2, wherein the hot cathode is an indirectly heatedtype hot cathode which has a cathode member which emits thermions by aheating and a filament which heats the cathode member, the cathodemember being arranged in an opening portion of the plasma generatingchamber, and a wall surface containing the opening portion of the plasmagenerating chamber is formed of an aluminum containing material, and isinsulated electrically from other wall surfaces of the plasma generatingchamber with intervention of an insulator and is set at a floatingpotential.
 11. An ion source according to claim 1, wherein the hotcathode is an indirectly heated type hot cathode which has a cathodemember which emits thermions by a heating and a filament which heats thecathode member, the cathode member being arranged in an opening portionof the plasma generating chamber, a wall surface containing the openingportion of the plasma generating chamber is formed of an aluminumcontaining material, and is insulated electrically from other wallsurfaces of the plasma generating chamber with intervention of aninsulator, and a voltage that is negative in contrast to the potentialof the plasma generating chamber is applied to the wall surface formedof the aluminum containing material.
 12. An ion source according toclaim 2, wherein the hot cathode is an indirectly heated type hotcathode which has a cathode member which emits thermions by a heatingand a filament which heats the cathode member, the cathode member beingarranged in an opening portion of the plasma generating chamber, a wallsurface containing the opening portion of the plasma generating chamberis formed of an aluminum containing material, and is insulatedelectrically from other wall surfaces of the plasma generating chamberwith intervention of an insulator, and a voltage that is negative incontrast to the potential of the plasma generating chamber is applied tothe wall surface formed of the aluminum containing material.
 13. An ionsource according to claim 1, wherein components of the opposingreflecting electrode consist of a composition different from that of theionization gas.
 14. An ion source according to claim 2, whereincomponents of the opposing reflecting electrode consist of a compositiondifferent from that of the ionization gas.